Hotend seems to be running hotter than reported

I've been printing lots of good looking prints of TPU on my V Minion for quite some time. Suddenly, I hear crackling during printing and get very rough looking prints with sagging bridges and rough porous walls. I lower the temp from 240 to 220 and then get decent looking prints again. And yes, I dry my filaments. This issue happened overnight. What's going on?